[Qemu-devel] [PATCH RFC 2/6] posix: add linux-only memfd fallback

["Marc-André Lureau" <marcandre.lureau@redhat.com>]

Implement memfd_create() fallback if not available in system libc.
memfd_create() is still not included in glibc today, atlhough it's been
available since Linux 3.17 in Oct 2014.

memfd has numerous advantages over traditional shm/mmap for ipc memory
sharing with fd handler, which we are going to make use of for
vhost-user logging memory in following patches.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 include/qemu/osdep.h | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 3247364..adc138b 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -6,6 +6,7 @@
 #include <stddef.h>
 #include <stdbool.h>
 #include <stdint.h>
+#include <unistd.h>
 #include <sys/types.h>
 #ifdef __OpenBSD__
 #include <sys/signal.h>
@@ -20,6 +21,64 @@
 
 #include <sys/time.h>
 
+#ifdef CONFIG_LINUX
+
+#ifndef F_LINUX_SPECIFIC_BASE
+#define F_LINUX_SPECIFIC_BASE 1024
+#endif
+
+#ifndef F_ADD_SEALS
+#define F_ADD_SEALS (F_LINUX_SPECIFIC_BASE + 9)
+#define F_GET_SEALS (F_LINUX_SPECIFIC_BASE + 10)
+
+#define F_SEAL_SEAL     0x0001  /* prevent further seals from being set */
+#define F_SEAL_SHRINK   0x0002  /* prevent file from shrinking */
+#define F_SEAL_GROW     0x0004  /* prevent file from growing */
+#define F_SEAL_WRITE    0x0008  /* prevent writes */
+#endif
+
+#ifndef MFD_ALLOW_SEALING
+#define MFD_ALLOW_SEALING 0x0002U
+#endif
+
+#ifndef MFD_CLOEXEC
+#define MFD_CLOEXEC 0x0001U
+#endif
+
+#ifndef __NR_memfd_create
+#  if defined __x86_64__
+#    define __NR_memfd_create 319
+#  elif defined __arm__
+#    define __NR_memfd_create 385
+#  elif defined __aarch64__
+#    define __NR_memfd_create 279
+#  elif defined _MIPS_SIM
+#    if _MIPS_SIM == _MIPS_SIM_ABI32
+#      define __NR_memfd_create 4354
+#    endif
+#    if _MIPS_SIM == _MIPS_SIM_NABI32
+#      define __NR_memfd_create 6318
+#    endif
+#    if _MIPS_SIM == _MIPS_SIM_ABI64
+#      define __NR_memfd_create 5314
+#    endif
+#  elif defined __i386__
+#    define __NR_memfd_create 356
+#  else
+#    warning "__NR_memfd_create unknown for your architecture"
+#    define __NR_memfd_create 0xffffffff
+#  endif
+#endif
+
+#ifndef CONFIG_MEMFD
+static inline int memfd_create(const char *name, unsigned int flags)
+{
+        return syscall(__NR_memfd_create, name, flags);
+}
+#endif
+
+#endif /* LINUX */
+
 #if defined(CONFIG_SOLARIS) && CONFIG_SOLARIS_VERSION < 10
 /* [u]int_fast*_t not in <sys/int_types.h> */
 typedef unsigned char           uint_fast8_t;
-- 
2.4.3